The present invention generally relates to resin compositions for use in laminating applications.
Polyetherester resins are a relatively new type of thermosetting resins being considered for use in a number of applications that have traditionally employed polyester and vinyl ester resins. Such applications include products for use in marine, transportation, and building industries, corrosion resistant products, as well as fiber or particulate reinforced products such as glass fiber reinforced laminate-type products.
Examples of processes for making polyetheresters are described in U.S. Pat. Nos. 5,319,006; 5,436,313; and 5,436,314. By adjusting the proportion of anhydride to polyol, the average polyether chain length between ester linkages and the crosslinkability of the polyester ether can be controlled. The viscosity and styrene content of a polyetherester resin are generally lower in comparison to conventional polyester resins containing isophthalic and terephthalic acids.
Notwithstanding any of the above efforts, physical properties of the polyetherester resins are typically not acceptable. Cured polyetherester thermoset resins often exhibit poor heat deflection temperatures under load (HDT), poor tensile and flex properties, and, more importantly, poor water resistance properties. Although not wishing to be bound by any theory, it is believed that these inferior properties are attributable to the fact that the polyetherester resins typically contain a high concentration of flexible and somewhat hydrophilic polyether linkages and a relatively low amount of rigid and hydrophobic aromatic ring structures on the polymer chain.
In view of the above, several attempts have been proposed to incorporate aromatic structures into the polyetheresters, typically by employing isophthalic acid. Examples of these attempts are described in U.S. Pat. Nos. 5,569,737; 5,610,205; 5,436,314; and 5,612,444. In spite of any potential benefits, there are several drawbacks to these processes. For example, it is often difficult to achieve a high reaction conversion. Moreover, it is difficult to obtain a resin having a low acid number (i.e., less than 30). A resin having a high acid number and a sizeable amount of carboxylic acid end groups can cause the cured resin to be excessively water sensitive and thus deteriorate quickly in aqueous or caustic conditions. It is believed that in order to potentially obtain a desirable balance of reactivity and physical properties, a relatively large amount of saturated aromatic esters should be incorporated in the polyetherester polymer chain. However, employing such aromatic groups often results in an increase in resin viscosity. Moreover, the tensile and flex properties and the heat distortion temperatures of the cured thermosets having aromatic groups are typically lower relative to a conventional polyester formed from isophthalic acid.
Attempts at reducing the acid number and improving the performance of the polyetherester resins have been proposed in U.S. Pat. Nos. 696,225 and 5,770,659. These patents generally propose methods of making polyetherester resins via chain extension of the polyetherester intermediate with a primary diol or an epoxy resin. These efforts, however, also suffer from potential drawbacks. For example, the molecular weight and thus the viscosity of the final resin typically increases dramatically as a result of the chain extension requiring higher levels of diluents to decrease such viscosities. These resins, and especially epoxy-modified polyetheresters, are thought to be particularly undesirable for VOC applications. Moreover, in order to reduce the resin acid number to below 30 and obtain adequate physical and chemical resistant properties, a relatively large quantity of epoxy is needed, typically more than 20 weight percent. Because such an epoxy is typically a very expensive raw material, this approach may not be attractive from a cost standpoint.
Other methods of forming modified polyetherester resins are proposed in U.S. Pat. Nos. 5,684,086 and 5,780,558. These references propose reacting dicyclopentadiene (DCPD) into the polymer backbone or blending DCPD with a polyetherester resin. This proposed technique is potentially a more cost effective technique at providing cured thermoset resins with improved strength properties. Nonetheless, these resins potentially display other inferior properties, particularly with respect to chemical resistance. The problems with these resins may be attributable to both DCPD and polyetherester resins exhibiting poor chemical resistance. Moreover, since a high level of DCPD resin is typically needed to provide adequate blend performance, an excess of DCPD may result in a thermoset resin that is very brittle.
In view of the above, there is a need in the art for a more cost-effective laminating resin that employs a reduced level of ethylenically unsaturated monomer (e.g., styrene) while displaying a desirable range of physical properties, particularly with respect to strength and chemical resistance.
In response to the above need and others, the present invention provides a polyetherester-based laminating resin composition. The composition comprises an unsaturated polyetherester resin and an epoxy acrylate oligomer. Advantageously, the composition comprises no greater than about 35 percent by weight of ethylenically unsaturated monomer while providing good physical properties particularly with respect to strength, toughness, and corrosion resistance.
The invention also provides an article of manufacture. The article of manufacture comprises the laminating resin composition and a fibrous substrate.
The invention will now be described in greater detail with respect to the preferred embodiments set forth herein below. It should be appreciated however that these embodiments are for illustrative purposes only, and that the scope of the invention is defined by the claims.
In one aspect, the invention relates to a polyetherester-based orxe2x80x94containing laminating resin composition. The laminating resin composition comprises an unsaturated polyetherester resin and an epoxy acrylate oligomer. The laminating resin comprises no greater than about 35 percent by weight of ethylenically unsaturated monomer. The laminating resin composition is thermosettable. The components of the laminating resin composition are preferably present in the form of a blend or mixture.
Any number of polyetherester resins may be used in the composition of the invention. Examples of unsaturated polyetherester resins and methods of making these materials are set forth in U.S. Pat. Nos. 5,696,225; 5,677,396; 5,436,313; and 5,319,006, the disclosures of which are incorporated herein by reference in their entirety. As an illustration, a polyetherester may be formed from a polyether reacting with an anhydride in the presence of a catalyst such as, for example, a protic acid or a metal salt of a protic acid, or a Lewis acid, in an amount suitable to promote insertion of the anhydride into the carbon-oxygen double bonds of the polyether to produce a polyetherester.
Polyethers suitable for use in the invention are preferably those derived from base or acid-catalyzed ring-opening polymerization of cyclic ethers such as epoxides, oxetanes, oxolanes, and the like. The polyethers have repeat units of oxyalkylene groups (xe2x80x94Oxe2x80x94Axe2x80x94) in which A preferably has from 2 to 10 carbon atoms, more preferably 2 to 4 carbon atoms. The polyethers can have different end groups, depending upon how the polyethers are made or modified. For example, the polyether can have hydroxyl, ester, ether acid, olefinic, or amino end groups, or the like, or combinations of these. Mixtures of different types of polyethers can be used.
Preferred polyethers are polyether polyols. Examples of polyether polyols include, but are not limited to, polyoxypropylene polyols, polyoxyethylene polyols, ethylene oxide-propylene oxide copolymers, polytetramethylene ether glycols, oxetane polyols, and copolymers of tetrahydrofuran and epoxides. Typically, these polyols with have average hydroxyl functionalities from about 2 to about 8.
Anhydrides that can be employed in the making of a polyetherester are preferably cyclic or acyclic, saturated or unsaturated. In a xe2x80x9ccyclicxe2x80x9d anhydride, the anhydride functionality is contained within a ring, such as in phthalic anhydride and maleic anhydride. xe2x80x9cAcyclicxe2x80x9d anhydrides, which include acetic anhydride, propionic anhydride, and the like, have no such ring. xe2x80x9cSaturatedxe2x80x9d anhydrides contain no ethylenic unsaturation, although they may contain aromatic rings. Phthalic anhydride, propionic anhydride, and succinic anhydride are examples of saturated anhydrides. xe2x80x9cUnsaturatedxe2x80x9d anhydrides contain ethylenic unsaturation. This unsaturation typically becomes incorporated into the polyetherester, and can be used for crosslinking. Examples include maleic anhydride, itaconic anhydride, and the like.
Specific examples of suitable anhydrides include, but are not limited to, acetic anhydride, propionic anhydride, maleic anhydride, phthalic anhydride, succinic anhydride, tetrahydrophthalic anhydride, citraconic anhydride, itaconic anhydride, and aryl-, alkyl-, and halogen-substituted derivatives of the above. Mixtures of these anhydrides may be used. The selection of the amounts of polyether and anhydride that may be used can be determined by the end user, and may depend, for example, upon the types of physical properties or degree of crosslinking that is desired.
The polyetherester resins of the invention preferably have a reduced number of saturated aromatic ester groups, preferably less than about 20 percent based on the number of unsaturated ester groups in the polyetherester resin and more preferably less than about 10 percent. The laminating resin composition may comprise various levels of polyetherester resin. Preferably, the laminating resin composition comprises from about 10 to about 70 percent by weight of the unsaturated polyetherester resin, and more preferably from about 20 to about 50 percent by weight.
Epoxy acrylate oligomers that are employed in the composition of the invention are known to those who are skilled in the art. As an example, the term xe2x80x9cepoxy acrylate oligomerxe2x80x9d may be defined for the purposes of the invention as a reaction product of acrylic acid and/or methacrylic acid with an epoxy resin. An anhydride (e.g., methacrylic anhydride) may also be employed with any of the above reactants in the formation of the epoxy acrylate oligomer. Examples of processes involving the making of epoxy acrylates can be found in U.S. Pat. Nos. 3,179,623; 3,367,992; 3,301,743; 3,256,226; the disclosures of which are incorporated herein by reference in its entirety. Epoxy resins that may be employed are known and include virtually any reaction product of a polyfunctional halohydrin, such as, but not limited to, epichlorohydrin, with a phenol or polyhydric phenol. Examples of phenols or polyhydric phenols include, but are not limited to, resorcinol, tetraphenol ethane, and various bisphenols such as Bisphenol-A, 4,4xe2x80x2-dihydroxy biphenyl, 4,4xe2x80x2-dihydroxydiphenylmethane, 2,2xe2x80x2-dihydroxydiphenyloxide, phenol or cresol formaldehyde condensates and the like. Mixtures of any of the above can be used. The preferred epoxy resins employed in forming the epoxy acrylates are those derived from bisphenol A, bisphenol F, especially preferred are their liquid condensates with epichlorohydrin having a molecular weight preferably in the range of from about 300 to about 800. The preferred epoxy acrylates that are employed of the general formula: 
where R1 and R2 is H or CH3 and n ranges from 0 to 1, more preferably from 0 to 0.3.
Other examples of epoxy acrylate oligomers that may be used include comparatively low viscosity epoxy acrylates. As an example, these materials can obtained by reaction of epichlorohydrin with the diglycidyl ether of an aliphatic diol or polyol. In a preferred embodiment, epoxy acrylates of the general formula can be used: 
wherein R3 is H, an aliphatic, cycloaliphatic or aromatic group containing C1 to C40 linear or branched, xcex1,xcex2-unsaturated straight or branched alkenyl or alkynyl, and may contain a group selected from C1-C20, Br, I, OR4, C(xe2x95x90O), OP(xe2x95x90O)R5, OP(xe2x95x90O)(OR5)2, OP(xe2x95x90O)OR5; wherein R4 is an alkyl from 1 to 20 carbon atoms in which each of the hydrogen atoms may be independently replaced by a halide; R5 is aryl or straight or branched C1-C20 alkyl group, and wherein the two R5 groups may be joined to form a 5- to 6-member heterocyclic ring, O, S, C(xe2x95x90O) or S(xe2x95x90O)2. As an example, suitable polyfunctional acrylates may include those described in ACS Polymer Preprints Vol. 38, page 84, 1997. A particularly preferred reaction involves a diepoxy, methacrylic anhydride, and methacrylic acid. A preferred diepoxy in this reaction is of the formula: 
A particularly preferred epoxy acrylate oligomer is an epoxy (meth)acrylate oligomer. Various quantities of epoxy acrylate oligomer may be used. Preferably, the laminating resin composition comprises from about 5 to about 50 percent by weight of epoxy acrylate monomer, and more preferably from about 20 to about 50 percent by weight.
In one embodiment, the laminating resin composition may further include a dicyclopentadiene (DCPD) resin. DCPD resins used in the composition of the invention are known to those skilled in the art. These resins are typically DCPD polyester resins and derivatives which may be made according to various accepted procedures. As an example, these resins may be made by reacting DCPD, ethylenically unsaturated dicarboxylic acids, and compounds having two groups wherein each contains a reactive hydrogen atom that is reactive with carboxylic acid groups. DCPD resins made from DCPD, maleic anhydride phthalic anhydride, isophthalic acid, terephthalic acid, adipic acid, water, and a glycol such as, but not limited to, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, dipropylene glycol, and poly-tetramethylene glycol, are particularly preferred for the purposes of the invention.
If employed, the DCPD resin may be used in various amounts in the laminating resin composition of the invention. Preferably, the laminating resin composition comprises from about 5 to about 50 weight percent of DCPD resin, and more preferably from about 20 to about 40 weight percent. Preferably, the DCPD resin has a number average molecular weight ranging from about 450 to about 1500, and more preferably from about 500 to about 1000. Additionally, the DCPD resin preferably has a ethylenically unsaturated monomer content of below 35 percent at an application viscosity of 500 cps.
In the event that the laminating resin composition employs an ethylenically unsaturated monomer such as, for example, a vinyl monomer, the laminating resin comprises no greater than about 35 percent by weight of such monomer. Applicants believe that employing no greater than 35 percent by weight of such a monomer may be potentially advantageous from an environmental standpoint relative to conventional resins. As known, the potential risk of any monomer often depends on various processing conditions relating to, for example, temperature, pressure, and monomer concentration. As an example, OSHA has suggested an allowable 8 hours time weight average styrene exposure level of 50 ppm. Such monomers may include those such as, for example, styrene and styrene derivatives such as alpha-methylstyrene, p-methyl styrene, divinyl benzene, divinyl toluene, ethyl styrene, vinyl toluene, tert-butyl styrene, monochlorostyrene, dichlorostyrene, vinyl benzyl chloride, fluorostyrene, and alkoxystyrenes (e.g., paramethoxystyrene). Other monomers which may be used include, for example, diallyl phthalate, hexyl acrylate, octyl acrylate, octyl methacrylate, diallyl itaconate, diallyl meleate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. Mixtures of the above may also be employed.
The laminating resin composition may also include other monomers if desired. For example, a suitable polyfunctional acrylate may be used in the laminating resin composition, including those described, for example, in U.S. Pat. No. 4,916,023 to Kawabata et al., the disclosure of which is incorporated by reference herein in its entirety. Such compounds include, but are not limited to, ethylene glycol (EG) dimethacrylate, butanediol demethacrylate, hydroxypropyl methacrylate, hydroxyethyl methacrylate, and the like. The polyfunctional acrylate which may be used in the present invention can be represented by the general formula: 
wherein at least four of the represented R""s present are (meth)acryloxy groups, with the remainder of the R""s being an organic group except (meth)acryloxy groups, and n is an integer from 1 to 5. Examples of polyfunctional acrylates include ethoxylated trimethyolpropane triacrylate, trimethyolpropane tri(meth)acrylate, trimethyolpropane triacrylate, trimethylolmethane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Mixtures of any of the above may be used in the laminating resin.
The laminating resin composition may include an agent such as an organic peroxide compound to facilitate curing of the composition. Exemplary organic peroxides may be used and include, for example, cumene hydroperoxide, methyl ethyl ketone peroxide, benzoyl peroxide, acetyl acetone peroxide, 2,5-dimethylhexane-2,5dihydroperoxide, tert-butyl peroxybenzoate, di-tert-butyl perphthalate, dicumylperoxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 2,5dimethyl-2,5bis(tert-butylperoxy)hexyne 3, bis(tert-butylperoxyisopropyl)benzene di-tert-butyl peroxide, 1,1-di(tert-amylperoxy)-cyclohexane, 1,1-di-(tert-butylperoxy)-3,3,5-trymethylcyclohexane, 1,1-di-(tert-butylperoxy)-cyclohexane, 2,2-di-(tert-butylperoxy)-butane, n-butyl 4,4di-(tert-butylperoxy)-valerate, ethyl 3,3-di-(tert-amylperoxy)-butyrate, ethyl 3,3-di-(tert-butylperoxy)-butyrate and the like. Mixtures of any of the above may be used. The agent is preferably employed in an amount from about 1 to 5 percent based on the weight of the laminating resin, more preferably from about 1 to 3 percent by weight, and most preferably from about 1 to 2 percent by weight.
Suitable curing accelerators or promoters may also be used and include, for example, cobalt naphthanate, cobalt octoate, N,N-dimethyl aniline, N,N-dimethyl acetamide, and N,N-dimethyl para-toluidine. Mixtures of the above may be used. These materials may be used in levels that may be determined by the end user.
Additional additives known by the skilled artisan may be employed in the laminating resin composition of the present invention including, for example, paraffins, fatty acids, fatty acid derivatives, lubricants, and shrink-reducing additives. Various percentages of these additives can be used in the laminating resin composition.
In another aspect, the invention relates to an article of manufacture. The article of manufacture may be a product which employs a laminating resin, and typically includes marine vessels, vehicles, and aircraft. More specifically, the article includes a substrate with the laminating resin composition coated thereon. The substrate may be made of any appropriate material and typically includes fibrous reinforced material such as those formed of thermoset or thermoplastic resins. The fibers which may be used typically include, but are not limited to, fibrous glass, carbon fibers, aromatic polyamide fibers, inorganic fibers, and the like.
The laminating resin composition may be prepared in accordance with various suitable processes known in the art and described further herein. Preferably, blends or mixtures of the invention may be prepared by combining a polyetherester resin with at least one epoxy acrylate oligomer. In certain embodiments, a DCPD resin may be included in the blend or mixture. As an example, the epoxy acrylate oligomer(s) can be either in monomer free liquid form or as a solution in a diluent such as, for example, styrene. Due to the typically excellent miscibility of the epoxy acrylate oligomer(s) with the polyetherester resin and also, if employed, DCPD resin, effective mixing can usually be accomplished by mixing either form of the epoxy acrylate oligomer(s) described above into the polyetherester resin, and DCPD resin if employed, namely the epoxy acrylate being monomer free or being present in a diluent. Employing conventional mixing equipment operating at ambient conditions is usually sufficient for the purposes of the invention.
In another aspect, the invention relates to a method of forming an article of manufacture. The method comprises applying a laminating resin composition described herein to a fibrous substrate to form an article of manufacture. The laminating resin composition may be applied to the fibrous substrate by a suitable method such as coating (e.g., spraying or brushing) to the substrate so as to form a coat. The processing conditions for applying the laminating resin composition along with the resulting thickness of the resin on the substrate may be selected according to the specific criteria of a person skilled in the art.
The laminating resin compositions of the invention may be used in a number of applications. Examples of suitable applications include, but are not limited to, corrosion resistant resins, Sheet Molding Compounding (SMC) resins, castings resins, radiation curable resins, pultrusion resins, gel coats, filament winding resins, hand lay-up, resin transfer molding, and prepregs.